SpeedFan is a program that monitors voltages, fan speeds and temperatures in computers with hardware monitor chips. SpeedFan can even access S.M.A.R.T. info and show hard disk temperatures. SpeedFan supports SCSI disks too.
It also has the ability to control fan speeds gradually on many motherboards and video cards to make your computer as silent as possible. This function needs administrator rights and the configuration can be a little complicated, but well worth it.